Fuel injection systems mix fuel with air in an internal combustion engine in response to a fueling command based on, for example, engine speed and torque. The process of determining the necessary amount of fuel, and its delivery into the engine, are known as fuel metering. Early injection systems used mechanical methods to meter fuel. Modern systems are nearly all electronic. An electronic engine control module (ECM) monitors engine operating parameters via various sensors. The ECM interprets these parameters in order to determine the fueling command that provides fueling amount and charge to be injected into the cylinders. The amount of injected fuel depends on conditions such as engine temperature, engine speed and torque.
The three elemental ingredients for combustion in an engine are fuel, air and ignition. To achieve stoichiometry, the fueling for a given set of conditions is estimated using tables based on inputs of engine speed and torque. These tables are calibrated for fuel injectors having certain established operating parameters, such as injection timing and rail pressures. During operation of the engine, the commanded fueling from these tables is selected based on, for example, engine speed and torque, to establish a fueling command in the ECM. The ECM then selects a combustion recipe comprising rail pressure, injector timings, charge references and other elements, which determines an expected fueling and charge into the cylinders from the fuel injectors for a given fueling command. Engine torque and speed are measured and provide feedback for adjusting the fueling command to achieve the desired torque and speed.
Ideally, the actual fueling into the cylinders corresponds to the expected fueling resulting from a fueling command so that engine output torque is known for a given fueling command. However, changes in operating conditions as well as changes and variations in injector performance, variability in the fuel system parts from engine to engine, and other factors can result in actual fueling varying from the expected fueling, otherwise known as fuel drift. Fuel drift causes a torque drift in the engine output and can negatively impact vehicle performance. For example, automatic manual transmissions use torque versus the fueling command models to determine shift patterns. Improper or non-optimal shift patterns may result due to the variation in actual fueling from expected fueling. Fuel economy broadcast accuracy is affected because the fueling command is used to estimate the fuel economy in real time. In addition, emissions increases can occur due to fueling parameter tables being tuned during engine calibration, and fuel drift results in the engine operating at a different point in the engine-fuel-speed map than the point at which the emissions reduction systems were calibrated for a given fueling command.
Thus, there remains a need for further contributions in this area of technology.